How do you store session data after phoning home?

My idea is to have a SaaS like extension. User open the browser, the browser check the installation and user rights and enable some of the functions to any extent. Good. I would not phone home every time the user performs an action and double check he is able to every single time.

Is it safe/ideal to store temp data in storage is there a temp storage or can I use session variable across my extension? Maybe a global variable or array?